167791-BIM-B-0606
Unitary Products Group
67
valve) clockwise to increase manifold pressure or
counterclockwise to decrease manifold pressure.
Be
sure not to under-fire the unit on first stage
.
9.
Once pressure has been checked, replace the plastic
cap covering the HI and LO pressure adjustment screws.
NOTE:
When using natural gas, the manifold pressure for
second stage (100% input) should be 3.5 IWG ±
0.3. The manifold pressure for first stage (60%
input) when using natural gas should be 1.5 IWG ±
0.3.
CHECKING GAS INPUT
NATURAL GAS
This unit has two stages of gas heat. The first stage is 60% of
the full fire input and is considered the minimum input for the
furnace. The intended input for each furnace is shown in the
table below. The following Table applies to units operating on
60 Hz power only.
To determine the rate of gas flow (Second Stage).
1.
Turn off all other gas appliances connected to the gas
meter.
2.
Turn on the furnace and make sure the thermostat is
calling for Second stage (100% input) heat.
3.
Measure the time needed for one revolution of the hand
on the smallest dial on the meter. A typical gas meter
has a 1/2 or a 1 cubic foot test dial.
4.
Using the number of seconds it takes for one revolution
of the dial, calculate the cubic feet of gas consumed per
hour. (See example below).
5.
If necessary, adjust the high pressure regulator as dis-
cussed in the section “Manifold Gas Pressure Adjust-
ment”.
Be sure not to over-fire
the furnace on Second
stage. If in doubt, it is better to leave the Second stage of
the furnace slightly under-fired. Repeat Steps 1-5.
To determine the rate of gas flow (First Stage)
1.
Turn off all other gas appliances connected to the gas
meter.
2.
Turn on the furnace and make sure the thermostat is
calling for first stage (60% input) heat.
3.
Even when the thermostat is calling for first stage heat,
the unit will light on second stage and will run on Second
stage for 1 minute. Allow this one-minute time period to
expire and be certain the unit is running on first stage.
4.
Measure the time needed for one revolution of the hand
on the smallest dial on the meter. A typical gas meter
has a 1/2 or a 1 cubic foot test dial.
5.
Using the number of seconds it takes for one revolution
of the dial, calculate the cubic feet of gas consumed per
hour (See example below).
6.
If necessary, adjust the low pressure regulator as dis-
cussed in the section “Manifold Gas Pressure Adjust-
ment”.
Be sure not to under-fire
the furnace on first
stage. If in doubt, it is better to leave the first stage of the
furnace slightly over-fired (greater than 60% input).
Repeat Steps 1-6.
NOTE:
To find the Btu input, multiply the number of cubic
feet of gas consumed per hour by the Btu content of
the gas in your particular locality (contact your gas
company for this information as it varies widely from
area to area).
TABLE 69: GAS HEAT STAGES
# of Burner Tubes
2nd Stage
Input (100%
Btuh)
1st Stage
Input (60%
Btuh)
4
120,000
72,000
6
180,000
108,000
8
240,000
144,000
TABLE 70: GAS RATE CUBIC FEET PER HOUR
Seconds
for One
Rev.
Size of Test Dial
1/2 cu. ft.
1 cu. ft.
10
180
360
12
150
300
14
129
257
16
113
225
18
100
200
20
90
180
22
82
164
24
75
150
26
69
138
28
64
129
30
60
120
32
56
113
34
53
106
36
50
100
38
47
95
40
45
90
42
43
86
44
41
82
46
39
78
48
37
75
50
36
72
52
35
69
54
34
67
56
32
64
58
31
62
60
30
60